Modeling changes in the state-of-charge open circuit voltage curve by using regressed parameters in a reduced order physics based model

Abstract

A method for modeling changes in the state of charge vs. open circuit voltage (SOC-OCV) curve for a lithium-ion battery cell as it ages. During battery pack charging, voltage and current data are gathered for a battery cell. A set of state equations are used to determine the stoichiometry and state of charge of the cathode half-cell based on the charging current profile over time. The voltage and current data, along with the stoichiometry and state of charge of the cathode half-cell, are then used to estimate maximum and minimum solid concentration values at the anode, using an error function parameter regression / optimization. With stoichiometric conditions at both the cathode and anode calculated, the cell's capacity and a new SOC-OCV curve can be determined.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]This invention relates generally to state of charge determination of cells in a battery pack and, more particularly, to a method for modeling changes in the state of charge vs. open circuit voltage curve for battery cells as the cells age, where the curve is modeled using parameter regression or optimization in a physics-based model, and the resulting cell performance curve is used to improve state of charge determination and capacity estimation.[0003]2. Discussion of the Related Art[0004]Electric vehicles and gasoline-electric or diesel-electric hybrid vehicles are rapidly gaining popularity in today's automotive marketplace. Electric and hybrid-electric vehicles offer several desirable features, such as reducing or eliminating emissions and petroleum-based fuel consumption at the consumer level, and potentially lower operating costs. A key subsystem of electric and hybrid-electric vehicles is the battery pack, which c...

AI Technical Summary

Benefits of technology

The present invention is about a method for monitoring changes in a lithium-ion battery cell's state of charge as it ages. This is done by measuring voltage and current data during charging, and using these data to calculate the relationship between the battery cell's state of charge and the amount of lithium present in the cathode half-cell. This relationship is then used to determine the cell's capacity and create a new SOC-OCV curve, which can be used to better estimate the cell's performance.

Problems solved by technology

A key subsystem of electric and hybrid-electric vehicles is the battery pack, which can represent a substantial proportion of the vehicle's cost.

Others of these methods simply estimate capacity fade, or reduction in energy storage capacity over time, but do not attempt to characterize the changes in the SOC-OCV curve.

However, none of the known methods uses in-vehicle measurements and a physics-based model to determine the actual physical state of the battery pack's cells, including the SOC-OCV curve, as the battery pack ages.

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